The current approach is to do this optimizations at a higher level,
in generic code, so that single-threaded cases can be specifically
targeted.
Furthermore, using IS_IN (libc) as a compile-time indicator that
all locks are private is no longer correct once process-shared lock
implementations are moved into libc.
The generic <lowlevellock.h> is not compatible with assembler code
(obviously), so it's necessary to remove two long-unused #includes.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
---
sysdeps/i386/nptl/pthread_spin_lock.S | 1 -
sysdeps/unix/sysv/linux/x86/lowlevellock.h | 87 ----------------------
sysdeps/x86_64/nptl/pthread_spin_lock.S | 1 -
3 files changed, 89 deletions(-)
delete mode 100644 sysdeps/unix/sysv/linux/x86/lowlevellock.h
@@ -16,7 +16,6 @@
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
-#include <lowlevellock.h>
ENTRY (pthread_spin_lock)
mov 4(%esp), %eax
deleted file mode 100644
@@ -1,87 +0,0 @@
-/* Low-level lock implementation, x86 version.
- Copyright (C) 2019-2021 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library; if not, see
- <https://www.gnu.org/licenses/>. */
-
-#ifndef _X86_64_LOWLEVELLOCK_H
-#define _X86_64_LOWLEVELLOCK_H 1
-
-#ifndef __ASSEMBLER__
-#include <sysdeps/nptl/lowlevellock.h>
-#include <single-thread.h>
-
-/* The lll_trylock, lll_lock, and lll_unlock implements a single-thread
- optimization using the cmpxchgl instruction. It checks if the process
- is single thread and avoid a more expensive atomic instruction. */
-
-/* The single-thread optimization only works for libc itself, we need
- atomicity for libpthread in case of shared futexes. */
-#if !IS_IN(libc)
-# define is_single_thread 0
-#else
-# define is_single_thread SINGLE_THREAD_P
-#endif
-
-/* In the __lllc_as we simply return the value in %eax after the cmpxchg
- instruction. In case the operation succeeded this value is zero. In case
- the operation failed, the cmpxchg instruction has loaded the current value
- of the memory work which is guaranteed to be nonzero. */
-static inline int
-__attribute__ ((always_inline))
-__lll_cas_lock (int *futex)
-{
- int ret;
- asm volatile ("cmpxchgl %2, %1"
- : "=a" (ret), "=m" (*futex)
- : "r" (1), "m" (*futex), "0" (0)
- : "memory");
- return ret;
-}
-
-#undef lll_trylock
-#define lll_trylock(lock) \
- ({ \
- int __ret; \
- if (is_single_thread) \
- __ret = __lll_cas_lock (&(lock)); \
- else \
- __ret = __lll_trylock (&(lock)); \
- __ret; \
- })
-
-#undef lll_lock
-#define lll_lock(lock, private) \
- ((void) \
- ({ \
- if (is_single_thread) \
- __lll_cas_lock (&(lock)); \
- else \
- __lll_lock (&(lock), private); \
- }))
-
-#undef lll_unlock
-#define lll_unlock(lock, private) \
- ((void) \
- ({ \
- if (is_single_thread) \
- (lock)--; \
- else \
- __lll_unlock (&(lock), private); \
- }))
-
-#endif /* !__ASSEMBLER__ */
-
-#endif /* lowlevellock.h */
@@ -15,7 +15,6 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
-#include <lowlevellock.h>
#include <sysdep.h>
ENTRY(pthread_spin_lock)